This invention relates to novel aminophosphonate-containing polymers, and their use as dispersants for concentrated aqueous particulate slurries, especially for titanium dioxide and kaolin, and as corrosion and scale inhibitors.
The preparation of similar polymers is disclosed in U.S. Pat. NO. 4,707,306 to Leighton, et al., which describes the synthesis of alpha-aminomethylene phosphonate betaines and polymers prepared therewith.
Most industrial waters contain alkaline earth metal cations, such as calcium, barium, magnesium, etc. and several anions such as bicarbonate, carbonate, sulfate, oxalate, phosphate, silicate, fluoride, etc. When combinations of these anions and cations are present in concentrations which exceed the solubility of their reaction products, precipitates form until these product solubility concentrations are no longer exceeded. For example, when the concentrations of calcium ion and carbonate ion exceed the solubility of the calcium carbonate reaction products, a solid phase of calcium carbonate will form.
Solubility product concentrations are exceeded for various reasons, such as partial evaporation of the water phase, change in pH, pressure or temperature, and the introduction of additional ions which form insoluble compounds with the ions already in the solution.
As these reaction products precipitate on surfaces of the water carrying system, they form scale or deposits. This accumulation prevents effective heat transfer, interferes with fluid flow, facilitates corrosive processes, and harbors bacteria. This scale formation is an expensive problem in many industrial water systems causing delays and shutdowns for cleaning and removal.
Scale-forming compounds can be prevented from precipitating by inactivating their cations with chelating or sequestering agents, so that the solubility of their reaction products is not exceeded. Generally, this requires large quantities of chelating or sequestering agents as cations, since chelation is a stoichiometric reaction, and these amounts are not always desirable or economical.
When a precipitation inhibitor is present in a potentially scale-forming system at a markedly lower concentration than that required for (stoichiometric) binding of the scale-forming cation, it is said to be present in "threshold" amounts, Hatch and Rice, "Industrial Engineering Chemistry", Vol. 31, pages 51 to 53 (January 1939); Reitemeier and Buehrer, "Journal of Physical Chemistry", Vol. 44, No. 5, pages 535 to 536 (May 1940); Fink and Richardson, U.S. Pat. No. 2,358,222; and Hatch, U.S. Pat. No. 2,539,305.
Certain water soluble polymers, including groups derived from acrylamide and acrylic acid have been used to condition water containing scale-forming compounds, as disclosed in U.S. Pat. Nos. 2,783,200; 3,514,476; 2,980,610; 3,285,886; 3,463,730; 3,518,204; and 4,604,212.
The problems associated with mineral scaling in cooling water systems have been known for many years. In such systems water flowing around heat exchange equipment deposits mineral scale on the surface of the installation. This scale builds up in layers giving an insulation effect, reducing the heat transfer of the apparatus and also resulting in poor water circulation. Eventually this necessitates the shut-down of the unit to allow mechanical or chemical cleaning.
Depositions in lines, heat exchange equipment, etc., may originate from several causes. For example, the precipitation of calcium carbonate and calcium phosphate will form scale, but products of corrosion also result in a deposit of iron oxide salts. These are deposited as scales due to changes in temperature, pH, concentration, pressure and incompatible water additives.
The development of high pH and/or non-chromate corrosion programs has increased the potential for scale formation due to chemical precipitation. In particular, since most of the treatments currently used include inorganic phosphate and/or low molecular weight, non polymeric phosphonic acid compounds, the reversion of the polyphosphates and the organic phosphates plus the use of high alkaline operating conditions leads to the formation and deposition of highly insoluble calcium phosphate.
Although steam generating systems are different from cooling water systems, they share common problems relating to calcium phosphate and iron oxide formation and other mineral scale deposition. In this regard, the formation of scale and sludge deposits on boiler heating surfaces is the most serious water problem encountered in steam generation. Although current industrial steam producing systems make use of external treatments of the boiler feed water to reduce scale forming ions, those operations are not totally effective and do not provide adequate treatment since muds, sludge, silts and hardness-imparting ions are not treated thereby, and eventually are introduced into the steam generating system.
Accordingly, internal treatment, i.e., the use of solubilizing chemicals which have the ability to keep the scale-forming materials in solution at concentrations substantially higher than would be expected are used throughout the industry in an attempt to alleviate the problems encountered by scale deposition. Solubilizing chemicals include alginates, lignins, lignosulfonates, tannins, carboxymethyl cellulose materials, and synthetic polymers such as polyacrylates and polymethacrylates.
Particulate matter, including, clays and pigments are employed in a variety of systems as fillers in plastics, rubbers, paper, fertilizers, herbicides, pesticides and animal feed; and as pigments in paints, rubbers, and paper coatings. For many applications, the particulate matter is shipped, stored, and/or applied in concentrated aqueous slurry form. Typically, the slurries have concentrations ranging from about 50-80% solids by weight. It is therefore a necessity that the slurry viscosity be as low as possible in order to afford ease of handling during pumping, admixing and application operations. A useful dispersant should be capable of providing stable low slurry viscosities, preferably over a wide usage range (e.g. minor fluctuations in dispersant concentration will not greatly affect slurry viscosity).
The prior art is replete with polymeric dispersants. U.S. Pat. No. 4,457,847 (issued July 3, 1984 to W. Lorenc, et al.) discloses a method of treating boiler water hardness with a water-soluble anionic vinyl polymer sequestrant containing at least 30% by weight carboxylate functionality. The Japanese Article "The Dispersion Applications of Copolymers from Sodium Vinyl Sulfonate", Sakaguchi and Nagase, Kogyo Kagaku Zasshi, Vol. 69 (1966) discloses the utility of low molecular weight sodium vinyl sulfonate-sodium acrylate copolymers as dispersants for low solids (e.g., 10%) kaolin clay and calcium carbonate aqueous slurries.
Australian Pat. application No. 37447/85 (published July 18, 1985) discloses various sodium hypophosphite modified acrylic acid copolymers. The cotelomers are described in general to be useful as boiler scale inhibitors, corrosion inhibitors in surface coating compositions for metal substrates, and as dispersants for china clay slurries.
Dispersants that are particularly useful for high solids pigment slurries have included inorganic polyphosphates such as sodium hexametaphosphate, sodium tripolyphosphate and potassium tripolyphosphate, and organic dispersing agents such as the sodium salt of polycarboxylic acid. U.S. Pat. No. 3,884,871 (issued May 20, 1975 to D. Herman). While the above polyphosphates are highly effective initially during the preparation of high solids slurries, upon aging or exposure to slightly elevated temperatures, they revert to orthophosphates which are ineffective as dispersants, thus resulting in high slurry viscosities.
U.S. Pat. No. 3,945,843 (issued Mar. 23, 1976 to D. Helty, et al.) describes the use of methyl acrylate-acrylic acid copolymers as dispersants for high solids suspensions of paper coating pigments such as calcium carbonate. The use of bisulfite-terminated oligomers as dispersants for high solids slurries of titanium dioxide and other particulate matter is described in U.S. Pat. No. 4,004,939 (issued Jan. 4, 1979 to R. DeColibus). Low molecular weight polyacrylic acid homopolymers and copolymers containing sulfonic acid groups which have polydispersities below 1.5 are described as useful pigment dispersants in European Patent Publication 129,329 (published Dec. 27, 1984).
Accordingly, an object of the present invention is to provide novel aminophosphonate-containing polymers. Another object of the invention is to provide a process of preparing said polymers. Still another object of the invention is to provide aminophosphonate polymers that are water soluble and water dispersible.
An additional object of the present invention is to provide a method of dispersing high solids particulate suspensions with the present novel polymer. Another object is to provide high particulate slurries which are low in viscosity and which have good stability after aging.
Still another object of the present invention is to provide a process for inhibiting corrosion and the formation and deposition of scale in aqueous systems with the present novel amino phosphonate-containing polymers.